Everybody knows that hydraulic pumps are expensive, especially closed
loop pumps. And everybody is aware that hydraulic circuits are
dirt-sensitive, especially closed loops. The ones who had already
performed the thrilling task of mounting a closed loop transmission (in
this case on board a BIG ship) which includes 180cc 200kg pumps, know
that it is time and effort consuming process. In fact, you should think
twice before you utter anything even remotely suggesting a slightest
possibility of having to remove the recently mounted "pumping unit", to
the team who had taken two full days just to fit it in place, with the
help of torch, hammer, the God and God knows what, if you want to keep
your health and looks intact. (yeah, I AM participating in "the longest
sentence contest", if you must know). Apart from time and effort, a
closed loop set-up consumes tons of money. That is why it is so
important to make sure that everything works OK first-time.
THE most important part of a closed circuit
start-up preparation is the THOROUGH cleaning and flushing of the
entire circuit. Most of the times a simple flushing procedure with
pressure filters and sensitive components by-passing is enough. I am
smiling now, I just said "simple flushing", it is never
simple. But sometimes, when the piping is extensive, welded or exposed
to the elements during several months construction process, used as
ash-tray/toilet during construction, you name it, a cleaning should be
yet thorough-er.
I, myself, have already performed such an exciting
super-flushing operation (on a fishing boat, by the way, it was a winch
driving circuit). We first used special acid solution pumped by an
external centrifugal pump, then an alkaline acid removing solution,
then water, then oil, then oil again, and lots and lots of F words
during the process... Believe me, the cost of those pumps (both on main
and auxiliary engines) and motors left no margin for error. The start
up went smoothly in a "by the book" fashion.
Nevertheless, sometimes the cleaning is overlooked.
Which is a feast for us, pump/motor guys, as in this case an expensive
overhaul is guaranteed! Check out the pics. This pump has around half
an our work time. In the end it stopped responding to the control
signal because the Pressure Control Pilot valve screen got completely
clogged (pic1),
creating the beautiful ballooned shape. Some measurements were made,
the PCP was dismounted from the control valve and the filter exposed.
At this time I suggested that further pump testing was senseless, and
still the client insisted on a bench test. O.K says I! PCP gets a new
filter, four hours later the pump responds to the external signal on
the test bench but looses charge pressure at 100 bar high. Well, told
you...
Exposing the insides revealed severe
contamination damage and many small metal balls, originated from
welding sparks. Want to take a wild guess on how the piping had been
made? (It was welded, dah!)
The pump, parts of which you see on the pics was the
first of a set of four.... all four went the same way... Quite a
kick in the nuts, don't you agree?
